Technical Field
Embodiments of the present disclosure are directed to semiconductor packages, including a package on package (PoP), and methods of making same.
Description of the Related Art
Reliability of semiconductor packages is of significant importance. Although various issues cause reliability problems in semiconductor packages, one known reason for reliability issues is that packages and the substrates or boards, onto which the package are mounted, are formed of various types of materials, each having different coefficients of thermal expansion (CTE). During use, heat is generated, and due to differing CTEs, stress may be introduced into the package and/or the board. The stress can cause cracks, for instance, in solder joints, such as those that couple the semiconductor package to a printed circuit board (PCB), thereby affecting board level reliability of the package by disrupting the electrical coupling between the package and the PCB.
Problems caused by differing CTEs may be further compounded when packages are stacked on top of each other, such as in stacked packages also referred to as a PoP. Typically in a PoP the stacked packages are coupled together by conductive balls located between adjacent packages. Each package may warp due to the stresses introduced into the package due to the differing CTEs. Furthermore, two adjacent packages may warp away from each other such that an upper package bows upward and a lower package bows downward, thereby placing the conductive balls in tensile stress, particularly, the conductive balls at the perimeter of the PoP. Additionally, as greater numbers of packages are stacked on top of each other, the stresses induced on the solder balls interconnecting the packages may increase.